To provide a position correction method and a position correcting device for achieving high focus precision even if a detection waveform is an asymmetric signal.

A position detector detects the position of a body to be exposed to light by applying light, and comprises a detection step that is a position correction method for correcting detected position information and detects a first waveform that is a position signal from the reflection light from the body to be exposed to light, a step for decomposing the first waveform and generating a plurality of second waveforms, and a step for removing a waveform containing a first asymmetric component from the plurality of second waveforms so that the first waveform becomes symmetrical and correcting the first waveform.